Sian Claire Owen, medical journalist for Cardio Debate, UK

Increased consumption of omega-6 polyunsaturated fat found in vegetable oils – specifically, omega-6 linoleic acid – has resulted in a corresponding increase in the prevalence of diabetes, obesity, asthma and coronary artery disease (CAD), according to an article recently published in the BMJ’s Open Heart journal. [1]

The authors highlight how a systematic review of studies that measured the levels of linoleic acid in adipose tissue in the USA, showed an increased from 9.1% in 1959 to 21.5% in 2008. In addition to diabetes and obesity, this increase was also associated with increased prevalence of CAD.

There is an extensive list of evidence that points to omega-6 vegetable oils as being a causative factor in atherosclerosis and CAD, including a meta-analysis of randomised controlled trials that found replacing saturated fat plus trans fat with omega-6 fats resulted in increases in all-cause mortality, ischaemic heart disease and cardiovascular disease mortality.

The authors also examined the mechanism behind the damaging effects of omega-6 linoleic acid. In a nutshell, Low-Density Lipoproteins (LDLs) must be oxidised (oxLDL) before they can inflict their toxic effects on the cells. This oxidation is an important step in the development of atherosclerosis, and it is well established that the oxidisation of linoleic acid within the LDL particle is the main culprit for this oxidisation. [1]

Therefore, the ‘oxodised linoleic acid theory of coronary artery disease’ is where the increased consumption of dietary linoleic acid is absorbed into all lipoproteins – not only LDL cholesterol, but VLDL and HDL cholesterols – and increases their propensity for oxidisation, which in turn increases the risk of developing CAD and CVD. [1]

To further back up their assertions, the Open Heart paper authors discussed previous clinical studies, which link increase consumption of dietary linoleic acid with an increased risk of CV mortality. For example, the MARGARIN study drew a correlation between linoleic-enhanced margarine and increased risk of CVD in hypercholesterolaemic men and women. [2] Another clinical study cited in this paper include the Anti-Coronary Club study from 1966, which showed that increased consumption of polyunsaturated fats compared with saturated fats resulted in increased heart disease mortality. [3]

The authors of the Open Heart paper conclude by stating how reducing dietary linoleic acid – mostly from industrial vegetable or seed oils – will reduce the risk of developing CAD and CHD. In the face of such mounting evidence, can we afford not to pay attention?

References

  1. DiNicholantonio JJ, O’Keefe JH. Omega-6 vegetable oils as a driver of coronary heart disease: the oxidised linoleic acid hypothesis. Open Heart 2018; 5: e000898.
  2. Bemelmans WJ, Broer J, Feskens EJ, et al., Effects of an increased intake of alpha-linoleic acid and group nutritional education on cardiovascular risk factors: The Mediterranean Alpha-Linoleic Enriched Groningen Dietary Intervention (MARGARIN) study. Am J Clin Nutr 2002; 75: 221-7.
  3. Christakis G, Rinzler SH, Archer M, et al. Effect of the anti-coronary club program on coronary artery disease. Risk-factor status. JAMA 1966; 198: 597-604.